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Your guide to managing acute renal failure

A Dr. Linda A. Ross at the 2007 American College of Veterinary Internal Medicine Forum in Seattle gave an excellent lecture on management of acute renal failure. Here are some relevant points:

Acute renal failure (ARF) is defined as the rapid loss (over hours to several days) of nephron function, resulting in azotemia, fluid, electrolyte and acid-base abnormalities and uremia.

Many causes have been identified in dogs and cats, the most common of which are ischemia (secondary to pancreatitis, shock, sepsis, DIC), toxicities (ethylene glycol; calciferol-containing rodenticides or human topical dermatological preparations; drugs such as aminoglycoside antibiotics, cisplatin, NSAIDs, and amphotericin B; lily plants in cats; and raisins or grapes in dogs); infections (leptospirosis, pyelonephritis), and nephroliths or ureteroliths causing obstruction to urine outflow.

Pathological stages

Acute renal failure is divided into three stages. The first (initiation) occurs during and immediately after insult to the kidneys, when pathological damage to the kidney is occurring. The latter part of the initiation phase has recently been termed the extension phase. During this time, ischemia, hypoxia, inflammation and cellular injury continue, leading to cellular apoptosis and/or necrosis. The initiation phase usually lasts less than 48 hours, during which time clinical and laboratory abnormalities may not be apparent.

The second stage (maintenance) is characterized by azotemia and/or uremia, and may last for days to weeks. Oliguria (<1.0 ml urine/kg body weight per hour) or anuria (no urine production) may occur during the maintenance stage; urine production can be highly variable.

The third stage is recovery, during which time azotemia improves and renal tubules undergo repair. Marked polyuria may occur during this stage as a result of partial restoration of renal tubular function, and of osmotic diuresis of accumulated solutes. Renal function may return to normal, or the animal may be left with residual renal dysfunction. It is possible for animals to have acute renal failure with sufficient tubular damage to cause polydipsia and polyuria, but not enough to cause azotemia.

Therapy

Treatment of ARF consists of specific therapy for the cause, as well as supportive therapy based on the stage of acute renal failure and the animal's fluid, electrolyte and acid-base status. It is important to remember that the doses of drugs excreted primarily by the kidneys should be reduced or the dosage interval extended in proportion to the degree of azotemia.

If the cause of ARF is known, specific therapy should be instituted. All animals should receive antibiotics effective against common uropathogens until infection is ruled out, and dogs may require antibiotics effective against leptospires, such as penicillin, amoxicillin or doxycycline.

Intravenous (IV) fluid therapy is the cornerstone of treatment for ARF, with the appropriate fluid type and amount determined by frequent monitoring of the animal's hydration status, renal function, acid-base status and electrolytes. The increasing availability of in-house or bedside blood chemistry analyzers facilitates such monitoring. Placement of a catheter in the jugular vein allows monitoring of central venous pressure and intravascular volume status. However, the jugular veins should be preserved for placement of a hemodialysis catheter if that is a treatment option, and not be used for IV catheters or even venipunctures for blood samples.

The initial volume of fluid to be administered should be calculated based upon the animal's body weight and degree of hydration. Water deficits should be replaced within four to six hours in order to restore renal blood flow to normal as soon as possible. Maintenance fluid requirements must be met (44 to 66 ml/kg daily), as well as estimated fluid losses from vomiting or diarrhea. Urine production should be monitored during the first few hours of fluid therapy. Placement of an indwelling urinary catheter is the most accurate method for this determination. However, the benefits of an indwelling catheter must be weighed against the risks of ascending infection, and in cats, sedation or anesthesia to place the catheter.